Despite enormous investments of financial and human resources, cancer remains one of the major causes of death. Current cancer therapies cure only about fifty percent of the patients who develop a malignant tumor. In most human malignancies, metastasis is the major cause of death.
Metastasis is the formation of a secondary tumor colony at a distant site. It is a multistep process of which tumor invasion is an early event. Tumor cells locally invade host tissue barriers, such as the epithelial basement membrane, to reach the interstitial stroma, where they gain access to blood vessels ("hematogenous metastasis") or lymphatic channels for further dissemination. After invading the endothelial layer of a vessel wall, the circulating tumor cells are dislodged into the circulation and arrest in the precapillary venules of the target organ by adherence to endothelial cell lumenal surfaces, or exposed basement membranes. The tumor cells again invade the vascular wall to enter the organ parenchyma. Finally, the extravasated tumor cell grows in a tissue different from where it originated.
Most cancer cells fail to survive in the circulation and it appears that normally the lining of blood vessels acts as a barrier to tumor cell extravasation. Endothelial injury or perturbation increases tumor metastasis. In addition, certain factors, such as cytokines, have been shown to substantially increase the adhesion of cancer cells to treated endothelium in vitro. Interleukin 1 (IL-1) and tumor necrosis factor (TNF), which are cytokines, each stimulate the biosynthesis and expression of a cell surface receptor called ELAM-1 (endothelial leukocyte adhesion molecule). ELAM-1 is a member of a family of calcium-dependent cell adhesion receptors, known as LEC-CAMs or selecting, which includes LECAM-1 and GMP-140 (also known as PADGEM or CD62). During an inflammatory response, ELAM-1 on endothelial cells functions as a "homing receptor" for leukocytes. Recently, ELAM-1 on endothelial cells was shown to mediate the increased adhesion of colon cancer cells to endothelium treated with cytokines (Rice and Bevilacqua, Science 246:1303-1306, 1989).
In most human malignancies, distant metastases are often too small to be detected at the time the primary tumor is treated. Furthermore, widespread initiation of metastatic colonies usually occurs before clinical symptoms of metastatic disease are evident. The size and age variation in metastases, their dispersed anatomical location, and their heterogeneous composition are all factors that hinder surgical removal and limit the concentration of anticancer drugs that can be delivered to the metastatic colonies. It has been estimated, for example, that in 1991 there will be over 60,000 deaths and over 150,000 new cases from just colorectal cancer in the U.S. alone.
Due to the difficulties in the current approaches to the treatment and prevention of metastases, there is a need in the art for improved methods and compositions for inhibiting metastasis mediated by endothelial adhesion molecules. The present invention fills this need, and further provides other related advantages.